As society becomes increasingly more dependent upon mobile devices (such as cell and smart phones, laptops, tablets, medical devices, and like hand-held and portable devices), high-power energy storage devices (such as batteries) are becoming increasingly in demand. An ideal battery for such devices would be designed to store sufficient energy to last for the useful life of the particular device, which lifetime could range from months to several years depending on the nature of the product (e.g. disposable cell phone, laptop computer, etc.).
For example, a cell phone typically draws between about 100 to 500 mw of power during operation, but an average battery can only store sufficient energy to drive the cell phone for approximately a day. The average cell phone battery stores roughly 1-5 watt-hours of energy which is typically dissipated during one day of average.
Similarly, tablet batteries store roughly 40-50 watt-hours of energy and last up to about 10 hours, indicating that the average power consumption is roughly 5 watts. Laptop computer batteries store roughly 75 watt-hours of energy and last approximately 5 hours, indicating that the average power consumption is roughly 15 watts. At the end of these time periods, it is necessary to recharge the battery to continue to use the device.
The average lifetime of a cell (or smart) phone is roughly 2 years. The lifetime of medical devices can range from one to several years. The average lifetime of a laptop (and by association, a tablet) is roughly 3 years.
Isotope-based power sources have been used to power certain types of electrical devices. For example, some isotope-based power generators convert the energy of alpha particles emitted from radioactive material into heat, which is then converted into useful energy like electricity. This is a thermoelectric conversion and is commonly used to power electrical devices used on deep space missions. In general, alpha particles used in this approach are fairly energetic (over 1 MeV) and can damage transistors. Hence, alpha-particle emitters are best used to create heat (by capturing the particle in a suitable material, such as a ceramic) and then converting that heat into electricity.
Another type of isotope-based power source converts the emission of beta-particles (electrons) into electricity. These are sometimes called betavoltaics. An example of a prior art betavoltaic power source is described in the article “Technology Today,” issue #1, 2011, and published at http://www.raytheon.com/technology_today/2011_i1/power.html.
Betavoltaic power sources have historically been useful where low power (tens of microwatts) is needed over many years (tens to hundreds of years). This is essentially a “solar cell” device (usually called a photovoltaic because it reacts to photons), but instead of using photons to create electron-hole pairs, the emitted “betas” (or high energy electrons) from the isotope create the hole-electron pairs. Betavoltaic power sources are used for deep space missions to produce energy at a few tens of a microwatt. For applications, which requires a life time of tens of years, the half-life of the isotope is often several decades, and (63)Ni with a half-life of 100 years is a preferred material.
Another use of isotope-based power sources is in the medical field where a low-power device (such as a pacemaker) is placed inside a patient. The pacemaker is generally inaccessible, and a long-life power source is advantageous. Because these devices are implanted within a patient, the total amount of emitted radiation must be very low, which in turn requires that the amount of power generated is low. For this application, the isotope thermoelectric generator has proven to be a successful product.
It would be desirable to have an isotope-based electrical power source that can generate sufficient power to drive a mobile device for the useful lifetime of the device without the need for recharging.